You could fill a book trying to define happiness, and another one for depression. In fact, there are already zillions, and mostly they don't agree with each other. Voting to close.
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FumbleFingersMay 27 '11 at 2:09

not too hard, no. It's just that EL&U is really after questions that can be answered precisely. Ideally with a yes/no or similar. This question could go on and on. It's really just an invitation to have a philosophical debate, which probably isn't what most people here want.
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FumbleFingersMay 27 '11 at 2:24

you might wish to consider that although the odd person suggests it now and again, there is no philosophy.se, because people who understand how stackexchange works will realise that particular one wouldn't (work).
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FumbleFingersMay 27 '11 at 2:27

@Fumble: there is one now: philosophy.stackexchange.com. But by your same argument, the OPs question wouldn't be a good fit there either.
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MitchDec 25 '11 at 13:22

3 Answers
3

Depression is an ambiguous term that can refer to a mood or mental disorder. Happiness can also be seen as a mood but is more commonly considered a state of mind.

One could plausibly make the argument that both depression and happiness are emotions or moods or states of mind. For them to serve as antonyms they would need to operate on the same domain. Unfortunately, they are both nearly impossible to define without using other emotions, moods, states of mind as comparators. The idea of defining them as antonyms, for example, would be more useful when determining whether someone was depressed or happy. But a more typical antonym for happiness is sadness and the antonym for depression is elation.

As for the terms being mutually exclusive, they can be if (a) working within the same domain and (b) are being defined that way for the purpose of determining which one someone is. But they aren't necessarily so. Someone who is clinically depressed could feel a moment of happiness or vice versa.

But in no domain, shared or otherwise, would the absence of one imply the presence of the other. Someone who is entirely apathetic wouldn't feel either.

The summary:

You can use "depression" and "happiness" as antonyms if you want but not everyone will agree with you

You can define them as mutually exclusive but not everyone will agree with you

The absence of one does not imply the presence of the other

(I am trying to ascertain the semantic validity of using depression-metrics as a gauge of happiness)

As for this goal, I recommend asking people in the fields of psychiatry and psychology instead of linguistics. We can tell you how people use the words; they can tell you about the actual moods and states of minds themselves. The odds are pretty good someone has an excellent answer to this intent but you aren't likely to find them here.